The present invention relates to a semiconductor laser capable of modulating laser oscillation at a frequency of 10 GHz or more.
One of the factors which determine the upper limit of the modulation frequency of a semiconductor laser, is the capacitance of the pn junction included in the laser. In order to reduce the junction capacitance, a laser structure has been devised in which semiconductor regions other than an active region indispensable for laser oscillation is etched off, and the remaining laser active layer is buried in a material having a dielectric constant smaller than that of the laser active layer (J. E. Bowers et al., Appl. Phys. Lett., Vol. 47, 1985, page 78). According to Bowers et al., however, a semiconductor crystal is buried in an SiO.sub.2 layer, and hence many crystal defects are generated in or on the semiconductor crystal. Thus, the above laser structure has a relatively short life, and is unfavorable from the practical point of view.